Tunisian authorities say that they have arrested seven people suspected of links to a deadly weekend attack that left one security officer dead and another injured.

The attacked occurred on Sunday in the Tunisian resort town of Sousse when perpetrators rammed their vehicle into security officers and attacked them with knives.

National guard spokesman Housameddine Jbabli said Monday on Radio Shems that seven suspects are being held by anti-terrorism authorities.

On Sunday, Tunisian forces fatally shot three alleged attackers. Among the seven detained is the wife of one of the dead attackers and the two brothers of another. Jbabli said that a preliminary investigation showed that the attackers had developed online links with foreign networks to find out how to make explosives.

Sousse was the site of Tunisia’s deadliest extremist attack in 2015, when a massacre killed 38 people, most of them British tourists. That attack dealt a heavy blow to Tunisia’s tourism sector, a pillar of the North African nation’s economy.